GRINDING METHOD AND APPARATUS

Abstract: In a grinding machine for cylindrical workpieces in which the workpiece (18) is rotated against a rotating grinding wheel (14), means (22) is provided for changing the speed of rotation of the workpiece and/or of the grinding wheel during the final stage of grinding. The speed change may comprise a deceleration of the grinding wheel, or a linear or sinusoidal reduction or increase in the workpiece speed, thereby reducing chatter-marks on the workpiece.

Description: Title Grinding Method and Apparatus Field of the invention This invention relates to a method of grinding a workpiece having a cylindrical surface and to apparatus for carrying out said method. Background to the invention It is well known that, when a cylindrical workpiece is being ground, the grinding process produces vibrations which generate lobes on the workpiece surface. This phenomenon is commonly known as chattering, and the resulting distortions on the workpiece are known as chatter-marks. To some extent chatter-marks can be reduced by absolute truing of the grinding wheel, but this is time consuming and expensive, especially when the grinding surface is a super-abrasive such as diamond or CBN. It is an object of the present invention to provide a method of and apparatus for reducing the tendency for generation of chatter-marks during grinding. The invention According to one aspect of the invention, there is provided a method of grinding- a cylindrical workpiece surface in which the speed of rotation of the grinding wheel and/or the speed of rotation of the workpiece is changed one or more times during the final stage of grinding, the period of such rotational speed variation including at least part of the final dwell period in which sizing occurs, thereby to reduce chatter-marks on the workpiece. According to another aspect of the invention, there is provided apparatus for grinding a cylindrical workpiece surface comprising a grinding machine having a grinding wheel, a grinding wheel feed, a grinding wheel feed controller, means for rotating the grinding wheel, a workpiece support and means for rotating the workpiece, a speed of rotation controller for the grinding wheel and for the workpiece, and means whereby, during the final stage of grinding extending into the final dwell period in which sizing occurs, the speed of rotation of the grinding wheel and/or the workpiece is changed one or more times in order to reduce chatter-marks on the workpiece. The method and apparatus of the invention may be applied to internal as well as external grinding. Moreover, it is to be noted that the speed variation effected is not dependent on vibration sensing of the grinding wheel or the workpiece. The rotational speed variation is preferably practised by rotational speed change which includes one or more changes in the rotational speed of the workpiece. If the speed variation includes change in the rotational speed of the grinding wheel, any change made will usually be decelerative. Preferably, however, the rotational speed of the grinding wheel is kept constant. The one or more rotational speed changes may be initiated either after a predetermined number of rotations of the workpiece where the number of turns per grinding cycle is controlled and/or at a predetermined feed distance before the feed position for final sizing, as indicated in more detail below. Thus, the possibilities for workspeed variation are limitless if its rotational speed is servo-controlled relative to time, grinding wheel feed position, component size and/or number of component turns. The speed variations effected may therefore be linear, reduce or increase at a rate relative to the above variables, or be of other controlled forms such as sinusoidal. However, the speed change is normally initiated during the slow approach to size feed and always extends into the final dwell period in which sizing occurs . Description of embodiment The practical implementation of the method and apparatus of the invention is exemplified with reference to the accompanying drawings, in which:- Figure 1 is a graph showing the feed of the grinding wheel in terms of workpiece distance v time; and Figure 2 is a much simplified diagram of a grinding machine . Figure 1 is a typical feed diagram for the grinding wheel in a grinding process for grinding a cylindrical workpiece. The grinding wheel feed includes a fine feed period 10 immediately prior to a stationary final dwell period 12 (size dwell) in which sizing occurs. In accordance with the invention, a change in the rotational speed of the workpiece is initiated in the fine feed period, and this speed change or one or more further speed changes is extended into at least part of the final dwell period 12. In the simplified grinding machine shown in Figure 2, wherein the grinding wheel is referenced 14, the wheel feed indicated at 16, the workpiece at 18 and the workpiece support at 20, a means 22 is incorporated for changing the rotational speed of the workpiece 18, as aforesaid. The means 22 is preferably constituted by a servo- controller, which automatically initiates one or more changes in the workspeed at the aforesaid time and for the aforesaid period, for example dependently on the feed position, the number of turns of the workpiece in the grinding cycle, and/or component size. The or each change effected is preferably not sudden, but is a relatively slow change which may be linear, sinusoidal or of any other desired form.

Claims: Claims : 1. A method of grinding a cylindrical workpiece surface in which the speed of rotation of the grinding wheel and/or the speed of rotation of the workpiece is changed one or more times during the final stage of grinding, the period of such rotational speed variation including at least part of the final dwell period in which sizing occurs, thereby to reduce chatter-marks on the workpiece. 2. Apparatus for grinding a cylindrical workpiece surface comprising a grinding machine having a grinding wheel, a grinding wheel feed, a grinding wheel feed controller, means for rotating the grinding wheel, a workpiece support and means for rotating the workpiece, a speed of rotation controller for the grinding wheel and/or for the workpiece, and means whereby, during the final stage of grinding extending into the final dwell period in which sizing occurs, the speed of rotation of the grinding wheel and/or the workpiece is changed one or more times in order to reduce chatter-marks on the workpiece. 3. A method according to claim 1 or apparatus according to claim 2 in which the rotational speed change includes one or more changes in the rotational speed of the workpiece. 4. A method or apparatus according to claim 1 or claim 2 in which the speed change is decelerative. 5. A method or apparatus according to any one of claims 1 to 4 in which the speed of the grinding wheel is kept constant . 6. A method or apparatus according to any one of claims 1 to 5 in which one or more rotational speed changes are initiated either after a predetermined number of rotations of the workpiece, where the number of turns per grinding cycle is controlled, and/or at a predetermined feed distance before the feed position for final sizing. 7. A method or apparatus according to any one of claims 1 to 5 in which the rotational speed is servo-controlled relative to time, grinding wheel feed position, component size and/or number of component turns. 8. A method or apparatus according to claim 6 or claim 7 in which the speed variations effected are linear or sinusoidal, and reduce or increase at a rate relative to the said variables. 9. A method or apparatus according to any one preceding claim in which the speed change is initiated during the slow approach to size feed. 10. A method of or apparatus for grinding a cylindrical workpiece substantially as herein described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawings.

Inventors: SMITH GEOFFREY IAN, SMITH, GEOFFREY, IAN
Applicants: SMITH GEOFFREY IAN, WESTERN ATLAS UK LTD, SMITH, GEOFFREY, IAN, WESTERN ATLAS U.K. LIMITED
Application year: 1994
Main classification: B24B1
IPC codes: B24B1, B24B41, B24B49